Magnetic sensors utilizing the GMR effect, frequently referred to as “spin valve” sensors, are known in the art. A spin valve sensor is typically a sandwiched structure consisting of two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the “pinned layer” because it is magnetically pinned or oriented in a fixed and unchanging direction by an adjacent anti-ferromagnetic layer, commonly referred to as the “pinning layer,” through anti-ferromagnetic exchange coupling. The other ferromagnetic layer is called the “free” or “unpinned” layer because the magnetization is allowed to rotate in response to the presence of external magnetic fields.
In a giant magnetoresistive sensor, a sense current is applied to the sensor and travels in the plane of the layers. In the presence of a magnetic field such as that provided by magnetic storage medium, the resistance of the sensor changes resulting in a change in voltage across the sensor due to the applied sense current. This voltage change may be measured and used to read back information. The operation of one configuration of a GMR sensor is described in U.S. Pat. No. 4,949,036, issued Aug. 14, 1990 to Grunberg, entitled “MAGNETIC FIELD SENSOR WITH FERROMAGNETIC THIN LAYERS HAVING MAGNETICALLY ANTIPARALLEL POLARIZED COMPONENTS”.
The increase in a real density of magnetic recording disks to values larger than 100 Gbit/in2 requires the development of new types of thin film read heads having a higher sensitivity than present spin valves. Currently spin valves are the most commonly used sensing device because they have a larger magnetoresistance (MR˜15-20%) as compared to conventional anisotropic magnetoresistance (AMR˜2%) devices. Furthermore, spin valves possess an intrinsic linear response allowing for a larger portion of the MR curve to be utilized while generating smaller harmonics in the output signal.
In recent years there has been a number of improvements to spin valve devices centered on the MR response. These developments include device size reduction, the addition of biasing layers, dual spin valve structures and tunnel junctions. Much of the research has focused on optimization of the MR properties as well. Specifically MR enhancement has resulted from varying layer thicknesses, “dusting” interfaces to improve the MR amplitude as well as structural stability upon annealing, and the addition of insulating layers to increase the specular reflection of the conduction electrons on outer surfaces of the layers. In all these cases, improvement of the MR response has come without fundamental changes in the device architecture and the materials set.
One material for use in giant magnetoresistive sensors that appears promising comprises Heusler alloy materials. However, attempts to implement giant magnetoresistive spin valve sensors using Heusler alloys have not met a great deal of success. The present invention provides a solution to this and other problems, and offers advantages over the prior art.